[FFmpeg-devel] [PATCH] Fixing HW accelerated decoders hanging or throwing error in h263dec

[Stefan Schoenefeld]

Hi Phil,

Unfortunately I cannot share the sample we use internally, but it should be reproducible with any h.263/mpeg-4 encoded file & hw accelerated decoding.

Thanks
Stefan

-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Philip Langdale
Sent: Saturday, August 3, 2019 08:57
To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] Fixing HW accelerated decoders hanging or throwing error in h263dec

On 2019-08-03 00:09, Timo Rothenpieler wrote:
> On 02.08.2019 11:18, Stefan Schoenefeld wrote:
>> Hi all,
>> 
>> Recently we encountered an issue when decoding a h.263 file:
>> 
>> FFmpeg will freeze when decoding h.263 video with NVDEC. Turns out 
>> this is not directly related to NVDEC but is a problem that shows 
>> with several other HW decoders like VDPAU, though the exact kind of 
>> error is different (either error messages or freezing[1]). The root 
>> cause is that ff_thread_finish_setup() is called twice per frame from 
>> ff_h263_decode_frame(). This is not supported by
>> ff_thread_finish_setup() and specifically checked for and warned 
>> against in the functions code. The issue is also specific to hw 
>> accelerated decoding only as the second call to
>> ff_thread_finish_setup() is only issued when hw acceleration is on. 
>> The fix is simple: add a check that the first call is only send when 
>> hw acceleration is off, and the second call only when hw acceleration 
>> is on (see attached patch). This works fine as far as I was able to 
>> test with vdpau and nvdec/nvcuvid hw decoding. The patch also adds 
>> NVDEC to the hw config list if available.
>> 
>> I also noticed a secondary issue when browsing through the code which 
>> is that, according to documentation, ff_thread_finish_setup() should 
>> only be called if the codec implements update_thread_context(), which 
>> h263dec does not. The patch does not address this and I'm not sure 
>> any action needs to be taken here at all.
>> 
>> Thanks,
>> Stefan
>> 
>> [1] This is depending on whether or not the hw decoder sets the 
>> HWACCEL_CAPS_ASYNC_SAFE flag
>> 
>>  From 0620ee777a8ba98145bb4781e30a77687c97dbf8 Mon Sep 17 00:00:00
>> 2001
>> From: Stefan Schoenefeld <sschoenefeld at nvidia.com>
>> Date: Fri, 2 Aug 2019 10:52:22 +0200
>> Subject: [PATCH] Fixing HW accelerated decoders hanging or throwing 
>> error messages in h263dec
>> 
>> ---
>> libavcodec/h263dec.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c index 
>> 6f001f6..8ee844e 100644
>> --- a/libavcodec/h263dec.c
>> +++ b/libavcodec/h263dec.c
>> @@ -614,7 +614,7 @@ retry:
>>       if ((ret = ff_mpv_frame_start(s, avctx)) < 0)
>>           return ret;
>> -    if (!s->divx_packed)
>> +    if (!s->divx_packed && !avctx->hwaccel)
>>           ff_thread_finish_setup(avctx);
> 
> This seems correct to me, but I'd like another pair of eyes to look 
> over it.

Seems fine to me as well.

> 
>>       if (avctx->hwaccel) {
>> @@ -747,6 +747,9 @@ const AVCodecHWConfigInternal 
>> *ff_h263_hw_config_list[] = { #if CONFIG_H263_VAAPI_HWACCEL
>>       HWACCEL_VAAPI(h263),
>> #endif
>> +#if CONFIG_MPEG4_NVDEC_HWACCEL
>> +    HWACCEL_NVDEC(mpeg4),
>> +#endif
> 
> Probably cleaner to split this into its own patch, but otherwise OK.
> 
>> #if CONFIG_MPEG4_VDPAU_HWACCEL
>>       HWACCEL_VDPAU(mpeg4),
>> #endif

Thanks for fixing this. I was always confused about whether h.263 was really supported by the hardware or not. Can you provide a link to a reference sample that fails without this change and succeeds with it?

--phil
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel at ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".

NVIDIA GmbH, Wuerselen, Germany, Amtsgericht Aachen, HRB 8361
Managing Director: Karen Theresa Burns

-----------------------------------------------------------------------------------
This email message is for the sole use of the intended recipient(s) and may contain
confidential information.  Any unauthorized review, use, disclosure or distribution
is prohibited.  If you are not the intended recipient, please contact the sender by
reply email and destroy all copies of the original message.
-----------------------------------------------------------------------------------